1. Field of the Invention
This invention relates to a light stabilization method for organic substrate materials and, more particularly, it relates to a method of stabilizing organic compounds, in particular, organic dyes to light.
2. Description of the Prior Art
In general, it is widely known that organic substrate materials such as organic dyes tend to fade or discolor by the action of light, and in the field of inks, textile dyeing, or color photography, various studies for preventing fading or discoloring of such organic dyes, that is, for improving the light fastness of these organic dyes have been made. This invention is used very advantageously for improving the light fastness or light stability of these organic substrate materials.
The term "organic substrate materials" or "substrate materials" as employed in this specification include materials which are colored or colorless to the human eye under sunlight and also include materials having simply an absorption maximum in the visible region, such as, for example, optical whitening agents, as well as the materials having the absorption maximum in an infrared region. Furthermore, the organic substrate materials which are the object of this invention include organic materials having their absorption maximum of about 300 nm in the ultraviolet region to about 800 nm in the infrared region. These organic substrate materials occur particularly in photographic materials, e.e., color films, prints, diffusion transfer units, etc., in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; fluorescent whitening agents; and dyes textiles, etc., and this invention is directed to improving the light fastness of these materials in each of these environments.
The term "dyestuff" or "dyes" as used in this specification include organic materials which are viewed by the human eye as colored materials under sunlight.
The term "light" used in this specification means electromagnetic radiation having a wavelength of shorter than about 800 nm and includes ultraviolet rays having wavelengths of shorter than about 400 nm, visible rays having wavelengths of from about 400 nm to about 700 nm, and infrared rays having wavelengths of from about 700 nm to about 800 nm.
Hitherto, it is well known that organic substrate materials such as coloring matters or dyes have a tendency to fade or discolor under the action of light and many methods have been reported for reducing the fading or discoloring tendency of these organic materials, that is, methods of improving the light fastness of the organic substrate materials. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indoaniline, azo and azomethine dyes to visible and ultraviolet light is improved by mixing therewith a phenol-type compound having a fused heterocyclic ring system.
In general, azomethine dyes or indoaniline dyes are formed by the reaction of oxidized aromatic primary amino developing agent and color photographic couplers and various methods for improving the stability of photographic images, i.e., color images are known in the field of silver halide photographic materials as described in Chapter 17 of C .E. K. Mees and T. H. James, The Theory of the Photographic Process, published in 1967 by Macmillan Co. For example, it is known the hydroquinone derivatives as described in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and British Pat. No. 1,363,921, the gallic acid derivatives as described in U.S. Pat. Nos. 3,457,079 and 3,069,262 and Japanese Patent Publication No. 13,496/68, the p-alkoxyphenols as described in U.S. Pat. Nos. 2,735,765 and 3,698,909, and the derivatives such as chroman and cumarone as described in U.S. Pat. Nos. 3,432,300, 3,573,050, 3,574,627, 3,764,337, 3,574,626, 3,698,909 and 4,015,990. However, while these compounds may have some effect as a fade preventing agent or discoloration preventing agent for color images, the effect is not sufficient.
Also, a method for improving the light stability of the organic substrate compounds using an azomethine quenching compound of which the absorption maximum is higher than the absorption maximum of the substrate material is described in British Pat. No. 1,451,000 but, since the azomethine quenching compound itself is strongly colored, the use of such a compound is disadvantageous in the point that it greatly influences the color hue of the substrate compounds.
Furthermore, in J. P. Guillory and R. S. Becker, J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974) and R. P. R. Ranawerra and G. Scott, J. Polym. Sci., Polym. Lett. Ed., 13, 71 (1975), the use of metal complexes for preventing the light deterioration of polymer is reported. Other stabilization methods of dyes by metal complexes are described in Japanese Patent Application (OPI) No. 87,649/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and Research Disclosure 15162 (1976). However, since the fade prevention effect of these complexes is not so high and the solubility of these complexes in organic solvents is low, it is difficult to add a sufficient amount of the complexes to obtain the desired fade prevention effect of them. Moreover, since these complexes themselves are greatly colored, these complexes suffer the disadvantage that if they are added in a large amount, they badly influence the purity and color hue of the organic substrate material, in particular dyes.
Furthermore, good fade preventing agents for cyan dyes have not been known.